Implantable medical devices and systems having inductive telemetry and recharge on a single coil

ABSTRACT

Implantable devices and related systems utilize a single coil for both inductive telemetry at one telemetry signal frequency and recharge at another recharge energy frequency. The coil is included in a tank circuit that may have a variable reactance. During telemetry, particularly outside of a recharge period, the reactance may be set so that the tank circuit is tuned to the telemetry frequency. During recharge, the reactance is set so that the tank circuit is tuned to the recharge frequency. Furthermore, the tank circuit may have a Q that is sufficiently small that the tank circuit receives telemetry frequency signals that can be decoded by a receiver while the tank is tuned to the recharge frequency so that telemetry for recharge status purposes may be done during the recharge period without changing the tuning of the tank circuit.

TECHNICAL FIELD

Embodiments relate to implantable medical devices that utilize inductivecouplings for telemetry and for recharge at one or more frequencies.More particularly, embodiments relate to implantable medical devicesthat use a shared coil for the telemetry and recharge applications.

BACKGROUND

Implantable medical devices (IMD) may provide a variety of differenttherapies and other functions including stimulation, drug infusion,physiological sensing, and the like. The IMDs receive programming froman external device and may also share information that has beencollected with the external device. Many IMDs communicate with theexternal device using an inductive form of telemetry where a telemetryhead is held in communication range of the IMD so that inductive signalsmay be exchanged.

The inductive downlink is obtained by a coil within the IMD that istuned to a telemetry frequency, e.g., 175 kilohertz, being emitted by acoil within the external device. Likewise, the inductive uplink isprovided by a coil within the IMD that is tuned to emit signals at atelemetry frequency of the coil of the external device. The uplink anddownlink telemetry frequencies are frequently the same and a single coilin each device is tuned to a single frequency that is used for both theuplink and the downlink.

Many IMDs operate on power from a battery, capacitor, or similar powersource and therefore have a limited lifetime of operation before areplacement or a recharge is necessary. For IMDs with a rechargeablepower source, the recharge energy may be received via an inductivecoupling. The external device has a coil tuned to a recharge frequency,e.g., 100 kilohertz, which may differ from the telemetry frequency. Manycommercially available IMDs have a second coil that is tuned to therecharge frequency being emitted by the external device.

While using two coils with the IMD adequately establishes telemetry andrecharge applications, the size occupied by two separate coils restrictsthe ability to make smaller IMDs. Thus, miniaturized IMD designs callfor a single coil such that the inclusion of the telemetry applicationprecludes inclusion of the recharge application.

SUMMARY

Embodiments address issues such as these and others by providing IMDsthat may include a single coil used for both telemetry and rechargeapplications. At least for some exchanges of information by telemetry,the IMD may utilize a tank circuit tuned to a recharge frequency ofrecharge energy to send and/or receive telemetry signals at a telemetryfrequency that is different than the recharge frequency.

Embodiments provide an implantable medical device that includes a tankcircuit tuned to a recharge frequency of recharge energy. Theimplantable medical device includes a receiver with at least one inputelectrically connected to a node of the tank circuit, the receiver beingconfigured to receive telemetry signals at a telemetry frequency whilethe tank circuit is tuned to the recharge frequency. The implantablemedical device includes a rechargeable power source and a rectifier thatis electrically connected between the rechargeable power source and thetank circuit and that is configured to receive the recharge energy atthe recharge frequency. The implantable medical device also includesmedical circuitry electrically connected to the rechargeable powersource.

Embodiments provide an implantable medical device that includes a tankcircuit tuned to a recharge frequency of recharge energy. Theimplantable medical device includes a driver circuit electricallyconnected to a node of the tank circuit, the driver circuit beingconfigured to produce telemetry signals at a telemetry frequency whilethe tank circuit is tuned to the recharge frequency. The implantablemedical device includes a rechargeable power source and a rectifier thatis electrically connected between the rechargeable power source and thetank circuit and is configured to receive the recharge energy at therecharge frequency. The implantable medical device includes medicalcircuitry electrically connected to the rechargeable power source.

Embodiments provide an external recharge device that includes a tankcircuit tuned to a recharge frequency of recharge energy. The externalrecharge device further includes a receiver with at least one inputelectrically connected to a node of the tank circuit, the receiver beingconfigured to receive from the tank circuit incoming telemetry signalsat a telemetry frequency. The external recharge device further includesa driver circuit electrically connected to a node of the tank circuit.Additionally, the external recharge device includes a controller inelectrical communication with the driver circuit, the controller causingthe driver circuit to drive the tank circuit at the recharge frequencywhen sending recharge energy and to drive the tank circuit at atelemetry frequency when sending outbound telemetry signals.

Embodiments provide a medical system that includes an external rechargedevice that transmits recharge energy at a recharge frequency from atank circuit tuned to the recharge frequency and that exchangestelemetry signals at a telemetry frequency that is different than therecharge frequency through the tank circuit tuned to the rechargefrequency. The medical system further includes an implantable medicaldevice that receives recharge energy at the recharge frequency from atank circuit tuned to the recharge frequency and that exchangestelemetry signals at the telemetry frequency through the tank circuittuned to the recharge frequency.

Embodiments provide a method of interaction with an implantable medicaldevice. The method involves, at the implantable medical device,receiving recharge energy at a recharge frequency from a tank circuit ofthe implantable medical device that is tuned to the recharge frequency.The method further involves, at the implantable medical device,exchanging telemetry signals at a telemetry frequency through the tankcircuit of the implantable medical device that is tuned to the rechargefrequency.

DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a typical operating environment for a medical systemincluding an external device and an IMD according to variousembodiments.

FIG. 2A shows a diagram of components of an example of an externaldevice.

FIG. 2B shows a diagram of components of an example of an externaldevice that utilizes a shared coil for recharge and telemetry.

FIG. 2C shows a diagram of components of an example of an externaldevice that interacts with the IMD via telemetry but does not performrecharge.

FIG. 3 shows a diagram of components of an example of an IMD.

FIG. 4 shows a diagram of a load branch and a recharge branch of anexample of an IMD.

FIG. 5 shows a circuit of one example of an IMD that provides fortelemetry uplink and telemetry downlink and recharge with a single coiland with a first receiver configuration and a first rectifierconfiguration.

FIG. 6 shows a circuit of one example of an IMD that provides fortelemetry uplink and telemetry downlink and recharge with a single coilwhile including a snubbing resistor for power management and/ortelemetry uplink.

FIG. 7 shows a circuit of one example of an IMD that provides fortelemetry uplink and telemetry downlink and recharge with a single coiland with a second receiver configuration.

FIG. 8 shows a circuit of one example of an IMD that provides fortelemetry uplink and telemetry downlink and recharge with a single coiland with a third receiver configuration.

FIG. 9 shows a circuit of one example of an IMD that provides fortelemetry uplink and telemetry downlink and recharge with a single coiland with a fourth receiver configuration.

FIG. 10 shows a circuit of one example of an IMD that provides fortelemetry uplink and telemetry downlink and recharge with a single coiland with a fifth receiver configuration.

FIG. 11 shows a circuit of one example of an IMD that provides fortelemetry uplink and telemetry downlink and recharge with a single coiland with a sixth receiver configuration.

FIG. 12 shows a circuit of one example of an IMD that provides fortelemetry uplink and telemetry downlink and recharge with a single coiland with a seventh receiver configuration.

FIG. 13 shows a circuit of one example of an IMD that provides fortelemetry uplink and telemetry downlink and recharge with a single coiland with an eighth receiver configuration.

FIG. 14 shows a circuit of one example of an IMD that provides fortelemetry uplink and telemetry downlink and recharge with a single coiland with a ninth receiver configuration.

FIG. 15 shows a circuit of one example of an IMD that provides fortelemetry uplink and telemetry downlink and recharge with a single coiland with a tenth receiver configuration.

FIG. 16 shows a circuit of one example of an IMD that provides fortelemetry uplink and telemetry downlink and recharge with a single coiland with an eleventh receiver configuration.

FIG. 17 shows a circuit of one example of an IMD that provides fortelemetry uplink and telemetry downlink and recharge with a single coiland with a second rectifier configuration.

FIG. 18 shows a circuit of one example of an IMD that provides fortelemetry uplink and recharge with a single coil.

FIG. 19 shows a circuit of one example of an IMD that provides fortelemetry downlink and recharge with a single coil.

FIG. 20 shows a state of switches of one example of an IMD to establishtelemetry uplink.

FIG. 21 shows an alternative state of switches of one example of an IMDto establish telemetry uplink.

FIG. 22 shows a circuit of one example of an IMD that provides fortelemetry uplink and telemetry downlink and recharge with a single coilhaving a tap that provides a voltage divider and with a first receiverconfiguration and a first rectifier configuration.

FIG. 23 shows a circuit of one example of an IMD that provides fortelemetry uplink and telemetry downlink and recharge with a single coiland with a second uplink configuration and a first rectifierconfiguration.

FIG. 24 shows a circuit of one example of an IMD that provides fortelemetry uplink and telemetry downlink and recharge with a singlecapacitor and a single coil providing variable inductance and with afirst receiver configuration and a first rectifier configuration.

FIG. 25 shows a circuit of one example of an external recharge devicethat provides for telemetry uplink and telemetry downlink and rechargewith a single coil and with a first receiver configuration.

FIG. 26 shows an example of logical operations that may be performed byan external recharge device and an implantable medical device that areinteracting by exchanging recharge energy and telemetry signals.

DETAILED DESCRIPTION

Embodiments provide for medical systems including IMDs that offer bothinductive telemetry and recharge applications using a single coil. Thetelemetry may include uplink, downlink, or both, and variousconfigurations for the telemetry may be provided with the single coil.Likewise, various configurations may be provided for the rechargeapplication, including various rectifier and power managementapproaches, while using the single coil.

FIG. 1 shows a typical operating environment for a medical system 100that includes an external device 102 and an IMD 108. The external device102 may provide programming and data collection services by usinginductive telemetry. The external device 102 may also provide rechargeservices by using an inductive coupling. A telemetry/recharge head 104that is tethered to the external device 102 may be placed nearby thepatient's body 114 and in communication range of the IMD 108 so that aninductive coupling occurs between a coil within the head 104 and thecoil within the IMD 108.

The head 104 may emit inductive signals 106 that represent downlinktelemetry signals or recharge signals. The telemetry signals are emittedat one frequency while the recharge signals are emitted at a differenttime and at another frequency. For instance, the telemetry signals maybe 175 kilohertz while the recharge signals are at 100 kilohertz.However, many different frequencies are possible for both telemetry andrecharge and the recharge frequency may either be of a higher or lowerfrequency than the telemetry. While a single external device 102 isshown for both telemetry and recharge applications, it will beappreciated that these applications may be provided by differentexternal devices where a first external device conducts a telemetrysession at the telemetry frequency and a second external device conductsa recharge session at the recharge frequency at some other time.

Furthermore, in some cases, one external device 102′ may provide arecharge function and may also provide a telemetry function thatoperates during a period of time when recharge is also being conductedwith pauses in the recharge while the telemetry takes place such as toconvey recharge status. In such cases, another external device 101 maybe present at other times to carry on a telemetry session for otherpurposes than recharge status, such as to program the IMD 108.

Embodiments of the IMD 108 may utilize the same coil for the downlinkand for the recharge. In such embodiments, the IMD 108 receives theinductive signals 106, including both the telemetry and the rechargesignals, on the coil. Embodiments of the IMD 108 may additionally oralternatively utilize the same coil for the uplink and for the recharge.In such embodiments, the IMD 108 emits inductive telemetry signals 112from the coil, and those signals are received by the coil of the head104.

The IMD 108 of this example includes an extension 110 such as a medicallead or a catheter that allows the IMD 108 to perform one or moremedical functions. For instance, where the extension 110 is a medicallead, then IMD 108 may provide stimulation signals to the body 114 viaelectrodes on the lead and/or may sense physiological signals of thebody 114 via the electrodes. Where the extension 110 is a catheter, theIMD 108 may infuse drugs into the body 114. These medical functions maybe performed by the IMD 108 in accordance with programming received viathe inductive telemetry signals and may be performed by using power froma rechargeable power source such as a battery or capacitor that isreplenished by the inductive recharge signals. While a battery isdiscussed below for purposes of illustration in relation to the severalembodiments, it will be appreciated that the embodiments may includeother rechargeable power sources in addition to or as an alternative toa battery.

FIG. 2A shows components of one example of the external device 102. Theexternal device 102 includes a processor/controller 202 andmemory/storage device(s) 204. The external device 102 may also includelocal input/output (I/O) ports 206 such as to provide local screendisplays and to receive user input via keyboard, mouse, and so forth.The external device 102 also includes a telemetry module 208 used toestablish the telemetry to the IMD 108, and the telemetry module 208 mayprovide signals at the telemetry frequency to the head 104 duringtelemetry sessions. The external device of this example also includes arecharge module 210 used to transfer recharge energy to the IMD 108, andthe recharge module 210 may provide signals at the recharge frequency tothe head 104 during recharge sessions.

The memory/storage devices 204 may be used to store information in useby the processor 202. For instance, the memory/storage 204 may storetherapy parameters that are input by a clinician or patient that are tobe downlinked into the IMD 104. The memory/storage devices 204 may alsostore programming that is used by the processor 202 to control thetelemetry and recharge actions of the external device 102. Thememory/storage devices 204 may be of various types, such as volatile,non-volatile, or a combination of the two. The memory storage devices204 may be used to store information for a long term and may be ofvarious types such as electronic, magnetic, and optical drives. Thememory/storage devices 204 are examples of computer readable media thatmay store information in the form of computer programming, datastructures, and the like.

The processor/controller 202 includes logic to perform variousoperations to allow telemetry and/or recharge sessions with the IMD 108.The processor/controller 202 may be of various forms. For instance, theprocessor/controller 202 may include a general-purpose programmableprocessor that executes software that is stored on the memory/storagedevices 204 or elsewhere. Other examples include a dedicated purposehardware circuit or hardwired digital logic. The processor/controller202 may communicate with the various other components through one ormore data buses.

The external recharge device 102 may include multiple tank circuits,each tank circuit having a coil with each tank circuit having adedicated purpose and frequency. For instance, one tank circuit may befor telemetry at a first frequency such as 175 kHz while another tankcircuit may be for recharge at a second frequency such as 100 kHz. Insuch a case, both coils of the tank circuits may be present within acommon enclosure so that the patient need only manipulate a singleenclosure in proximity to the IMD 108 to enable both telemetry andrecharge. As an alternative, the external recharge device 102 mayinclude a single tank circuit and coil where the tank circuit may betuned to the appropriate frequency of the signal being sent or receivedat any given moment.

For some embodiments, the external recharge device 102 may send andreceive telemetry signals that are during a period of recharge. So,while the tank circuit may be tuned to the recharge frequency foroptimal recharge coupling, the external device 102 may periodicallypause the recharge in order to exchange telemetry signals related to therecharge status. In one embodiment, the external recharge device 102 mayutilize a dedicated telemetry tank circuit for the telemetry if soequipped. In another embodiment that includes a single tank circuit, theexternal recharge device 102 may tune the tank circuit to the telemetryfrequency if the external recharge device 102 is equipped to tune thetank circuit.

In yet another embodiment, the external recharge device 102′ as shown inFIG. 2B may include the same components as the external recharger device102 above except that this external recharger device 102′ may besimplified by having within the head 104′ a coil circuit 212 thatincludes the single tank circuit with fixed tuning. The single tankcircuit may have fixed tuning, for instance tuned to the rechargefrequency even though the external recharge device 102′ may communicatevia telemetry signals with the IMD 108 such as during a period ofrecharge. The telemetry uplink circuit 208′ includes a receiver while arecharge/telemetry downlink circuit 210′ includes a driver that maydrive the tank circuit at either the recharge frequency for rechargepurposes or the telemetry frequency for telemetry purposes. Additionaldetails for the construction of this example of an external rechargerdevice 102′ are discussed in more detail below with respect to FIGS. 25and 26.

This embodiment in FIG. 2B may have a relatively high Q tank circuit,such as a Q of about 200 for example which is beneficial fortransmitting recharge energy and/or telemetry signals. However, asdiscussed below in relation to FIG. 25, the external recharger mayinclude the ability to de-Q the tank circuit by adding impedance duringreception of telemetry signals to widen the bandwidth which allows thetank circuit to adequately couple at a telemetry frequency that differsfrom the tuned frequency. For example, the tank circuit may adequatelycouple with a coil of an IMD 108 at a telemetry frequency of 175 kHzwhile the tank circuit of the external recharge device 102′ is tuned to100 kHz. This allows the external recharge device 102′ to have arelatively simple construction while being able to exchange telemetrysignals with the IMD 108 during a period of recharge without the need toconfigure telemetry via a different coil or via a change of tuning ofthe single coil. This in turn reduces the amount of time to exchange thetelemetry signals and thereby reduces the amount of time needed tocomplete a recharge of the IMD 108.

FIG. 2C shows an example of the external telemetry device 101 that isused to communicate via telemetry signals with the IMD 108 at timesother than during a recharge period. The external telemetry device 101may include some of the same components as the external recharger device102 above, including a controller 222, memory and storage 224, I/O 226,and a telemetry circuit 228. This external telemetry device 102 may omitthe ability to provide recharge energy such as by being configured todrive a tank circuit having a coil within the head 230 at only thetelemetry frequency.

FIG. 3 shows components of one example of the IMD 108. The IMD 108includes a processor/controller 302 and a memory/storage device(s) 304.The IMD 108 also includes medical circuitry 306 that performs a medicaltask such as stimulation, drug delivery, monitoring, and the like. TheIMD 108 also includes telemetry circuitry 308 used to establish theuplink and/or downlink telemetry with the external device 102 inconjunction with single coil circuitry 312. The IMD 108 further includesrecharge circuitry 310 used to receive recharge energy from the externaldevice 102 in conjunction with the single coil circuitry 312.

The memory/storage devices 304 may be used to store information in useby the processor/controller 302 such as programming and data values. Thememory/storage devices 304 may store additional information includingtherapy parameters that are used to control the medical circuitry 306.The memory/storage devices 304 may be of various types such as volatile,non-volatile, or a combination of the two. The memory/storage devices304 are also an example of computer readable media that may storeinformation in the form of computer programming, data structures, andthe like.

The processor/controller 302 includes logic to perform operations thatallow telemetry and recharge sessions with the external device 102 to beestablished. The processor/controller 302 may be of various forms likethose discussed above for the processor/controller 202 of the externaldevice 102, such as a general purpose processor, an application specificcircuit, hardwired digital logic, and the like. The processor/controller302 may communicate with the various other components through one ormore data buses. The processor/controller 302 may also control siliconbased switches that are either integral to the processor/controller 302or separate electronic devices to provide the telemetry, recharge, andpower management functions while using the single coil. These switchesand other circuit details are discussed in more detail below withreference to FIGS. 4-24.

For some embodiments, the IMD 108 may send and receive telemetry signalsduring a period of recharge. So, while the tank circuit may be tuned tothe recharge frequency for optimal recharge coupling to the externalrecharge device, the IMD 108 may listen for and periodically exchangetelemetry signals related to the recharge status such as in response toa request by the external recharge device. In one embodiment thatincludes a single tank circuit, the IMD 108 may tune the tank circuit tothe telemetry frequency.

In yet another embodiment, the IMD 108 may maintain the tuning for bothrecharge energy and telemetry during a recharge period. For instance,the tank circuit of the IMD 108 may be tuned to the recharge frequencyeven though the IMD 108 may communicate via telemetry signals with theexternal recharge device during a period of recharge.

In contrast to the external recharge device 102′, embodiments of the IMD108 may rely on a relatively low Q tank circuit, such as for example a Qin the range of 2 to 6 that may be achieved by the interaction of thecoil of the tank circuit and the metal or other conductive material ofthe enclosure of the IMD 108 that includes the coil. As a specificexample, with a hermetically sealed, titanium shell, the Q of a 500 μHcoil within a ˜3 cc IMD 108 with 0.008″ Grade-5 Titanium shields isapproximately 3. This relatively low Q provides a wide bandwidth andallows the tank circuit to adequately couple at a telemetry frequencythat differs from the tuned frequency. For example, the tank circuit mayadequately couple with a coil of an external recharge device at atelemetry frequency of 175 kHz while the tank circuit of the IMD 108 istuned to 100 kHz. This allows the IMD 108 to exchange telemetry signalswith the external recharge device during a period of recharge withoutthe need to configure telemetry via a different coil or via a change oftuning of the single coil. This in turn reduces the amount of time toexchange the telemetry signals and thereby reduces the amount of timeneeded to complete a recharge.

In an application where the recharge frequency is 100 kHz and thetelemetry frequency is 175 kHz, a receiver of the telemetry circuitry308 with suitable out-of-band aggressor performance, utilizingsynchronous demodulation for instance, may detect a coupled 175 kHztelemetry signal on a 100 kHz tuned coil, especially if the signal islarge due to good coupling and/or a large signal on the primary. In thesame example, the H-bridge circuit may be used to drive the tank at 175kHz. This signal may in turn be sensed by a receiver of the externalrecharge device 102′ discussed above which also possesses sufficientsensitivity and frequency selectivity.

The converse is also true. If the tank circuit is tuned to the telemetryfrequency of 175 kHz, recharge energy at 100 kHz may be still be coupledonto the coil of the tank circuit within the IMD 108 and flow through arectifier to recharge the battery or other rechargeable power source.Thus, in some embodiments, the external device 100 may be configured toemit 100 kHz energy via a tank circuit tuned to 175 kHz in certainsituations such as when the IMD 108 has a low battery and a rechargedevice 102, 102′ is not available. In that case, the IMD 108 being tunedto 175 kHz receives the 100 kHz energy to provide some degree ofrecharge which may then allow the external device 101 to subsequentlycommunicate with the IMD 108 without the IMD 108 reaching a depletedbattery condition.

FIG. 4 shows one example of a configuration 400 of circuit modules thatmay be employed in various embodiments of the IMD 108. Thisconfiguration 400 includes a battery 402 that provides the energy forthe general operation of the IMD 108 including the operations beingperformed by the logic of the processor/controller 302 and the medicaltasks being performed by the medical circuitry 306. The battery 402 alsoreceives the energy being collected during the recharge session.

As shown, there is a load branch stemming from a node 408 and a rechargebranch stemming from a node 410, where the node 408 and node 410 stemfrom the battery 402. In this example, each branch includes a Coulombcounter, 404, 406 where the Coulomb counter 404 for the load branchmeasures the amount of charge leaving the battery while the Coulombcounter 406 for the recharge branch measures the amount of chargeentering the battery. The processor/controller 302 may gather thisinformation to monitor the condition of the battery 402 as well as toreport such information to the external device 102.

The node 408 sources power to several components. Theprocessor/controller 302 receives power to operate includingimplementing the logic and output to control various switches that varythe tuning frequency of the coil and select between uplink, downlink,and recharge modes. Drive circuitry such as an oscillator, for instancea sinusoidal power amplifier, or such as a set of transmitter switches414 receive power to ultimately ring the coil to emit telemetry signals.A receiver 412 consumes power to receive and amplify the downlinktelemetry signal and return it to the controller 302. The medicalcircuitry 306 receives power to perform the medical tasks such as pulsegeneration, drug infusion, data collection, and the like.

Several components receive control signals from the processor/controller302. The drive circuitry 414 may receive an activation signal in thecase of an oscillator. The drive circuitry may receive timed controlsignals, discussed in more detail below with reference to FIGS. 20 and21, in the case of transmitter switches that alternate their states inorder to ring the coil at the telemetry frequency to uplink telemetrysignals. A set of receiver switches 424 receive control signals toachieve a state that allows detection of the telemetry signal of thecoil at the receiver 412. A tuning switch 420 receives a control signalto alter the state and ultimately vary the reactance of a tank circuit416 that includes the coil so that one state tunes the tank circuit 416to a telemetry frequency while another state tunes the tank circuit 416to a recharge frequency.

The node 410 of the recharge branch receives power from a power module418. This power module 418 receives the recharge signal induced onto thecoil of the tank circuit 416 by the incoming recharge signals. The powermodule 418 includes a rectifier, a filter, and a limiter so that thenode 410 receives power that has a suitable voltage and current forrecharging the battery 402.

The various switching modules of FIG. 4 have a default state such aswhere no control signal is present either by operation of theprocessor/controller 302 or as a result of a fully depleted battery 402.One configuration of the switches is such that when all switches are inthe default state, the tank circuit 416 is tuned to the telemetryfrequency with the tank circuit's output being directed into therectifier of the power module 418. Thus, an attempt at communicatingwith the IMD 108 that is currently non-operational via telemetry maysucceed in supplying enough recharge energy to the battery 402 to allowthe processor/controller 302 to become operational and respond.

Examples of specific circuits such as those that are shown in FIGS. 5-19and 22-24 and others that are discussed below implement the modules ofFIG. 4 while providing the default state that allows for recharge at thetelemetry frequency. FIG. 5 shows a first configuration 500 for acircuit that provides for telemetry uplink and downlink at a telemetryfrequency with the tank circuit tuned to the telemetry frequency such asto allow for arm's length coupling. The configuration 500 also providesfor recharge with power management at a recharge frequency that isdifferent than the telemetry frequency with the tank circuit tuned tothe recharge frequency while using a single coil. Additionally, thefirst configuration 500 allows for telemetry uplink and downlink at thetelemetry frequency during a recharge period while the tank circuitremains tuned to the recharge frequency. As discussed above, the firstconfiguration 500 includes switches implemented in silicon with adefault state that is open which allows for recharge mode to occur atthe telemetry frequency when the IMD 108 is non-operational due to adepleted battery.

The first configuration includes the tank circuit 416 that has a coil504 and the variable reactance is provided by a variable capacitance.The variable capacitance is achieved in this example by providing afirst capacitor 506 that is hardwired in series with the coil 504 and byproviding a second capacitor 510 that is switched into and out of aparallel relationship with the first capacitor 506 by a tuning switch518, which is implemented in silicon and is under the control of theprocessor/controller 302. The processor/controller 302 may open andclose the tuning switch 518 to vary the capacitance of the tank circuitand thereby tune the resonant frequency of the tank circuit 416 toeither the telemetry or the recharge frequency.

In this particular example, the telemetry frequency is higher than therecharge frequency and so the coil 504 is tuned to the telemetryfrequency when less capacitance is present. It will be appreciated thatthe opposite design could be employed where the recharge frequency ishigher and thus some capacitance is switched out of the circuit to tunethe coil 504 to the recharge frequency.

The tank circuit 416 establishes several nodes. An inductor side node528, a capacitor side node 526, and a high voltage node 508 areachieved. The high voltage node 508 acquires a relatively high voltageperiodically as the voltage swings within the tank circuit 416. Anadditional capacitor side node 512 is present particularly when thetuning switch 518 is open.

The capacitor side node 526 and inductor side node 528 are connected toa rectifier that is established by a set of diodes 536, 538, 540, and542 that may be of the Schottky variety. These diodes form a full-bridgerectifier. However, a capacitor low side switch 522 and an inductor lowside switch 524 are present and either one may be closed by theprocessor/controller 302 to provide a half-wave rectifier.

As an alternative rectifier for this configuration, the capacitor lowside switch 522 and the inductor low side switch 524 may be operated aslow-side synchronous rectifier switches. In such a case, the statemachine control of these switches 522, 524 by the processor/controller302 operates by closing the capacitor low side switch 522 while leavingthe inductor low side switch 524 open when the inductor side node 528flies high and by closing the inductor low side switch 524 while leavingthe capacitor low side switch 522 open when the capacitor side node 526flies high. Other rectifier options are discussed with reference toother circuit diagrams below.

A capacitor side Zener diode 544 and an inductor side Zener diode 546are also present. These devices limit voltage swings on the capacitorside node 526 and the inductor side node 528 to prevent over-voltagedamage from occurring on voltage sensitive devices connected to thesenodes. Voltage sensitive devices may include the various switches whichare implemented in silicon and particularly those that are implementedas monolithic devices. Likewise, Zener diodes 514 and 516, shown in ananode-to-anode relationship but could be in a cathode-to-cathoderelationship, are present to prevent over-voltage damage from occurringon additional voltage sensitive devices such as the tuning switch 518 onthe additional capacitor side node 512. These devices may be actualZener diodes or may be other devices which have Zener-like behavior.

The high voltage node 508 achieves the highest voltage during voltageswings within the tank circuit 416. As can be seen, no voltage sensitivedevice is DC coupled to the high voltage node which reduces thelikelihood of any damage to those voltage sensitive devices. While theadditional capacitor side node 512 may also achieve the relatively highvoltage during telemetry by being AC coupled to the high voltage node508 via the second capacitor 510 while the turning switch 518 is open,the Zener diodes 514, 516 provide additional protection for the tuningswitch 518.

The rectifier provides voltage to a rectifier recharge node 550. Thisrectifier recharge node 550 also includes a filtering capacitor 548 inparallel with the rectifier. A current or voltage limiter 552 is inseries between the rectifier recharge node 550 and the battery rechargenode 410 to prevent the battery 402 from receiving voltage and/orcurrent in excess of the amounts rated for the battery 402.

This embodiment of the IMD 108 is also capable of telemetry downlink byusing the tank circuit 416. The receiver 412 is present to receive thetelemetry signals induced on the coil 504. The receiver 412 is connectedto the tank circuit in a first configuration in the example of FIG. 5.Other configurations are discussed below with reference to otherfigures. In this example, a first input of the receiver 412 is connectedto the inductor side node 528 while a second input of the receiver 412is connected to the additional capacitor side node 512. In this mannerthe second input of the receiver 412 is capacitively coupled to the highvoltage node 508 via the second capacitor 510 regardless of the state ofthe tuning switch 518. As the input impedance of the receiver 412 isvery high, the receiver 412 does not appreciably affect the tuning ofthe tank circuit 416.

A tank switch 520 is included between the capacitor side node 526 andthe inductor side node 528. This tank switch 520 when closed caneffectively bypass the rectifier during the downlink telemetry. Otheroptions for downlink telemetry where the tank switch 520 is left open oromitted are discussed below in relation to other figures.

This embodiment of the IMD 108 is also capable of telemetry uplink byusing the tank circuit 416 and one of various methods. For instance, asshown, an H-bridge may be provided in relation to the tank circuit 416by connecting a capacitor high side switch 530 between the load node 408and the capacitor side node 526 while also connecting an inductor highside switch 532 between the load node 408 and the inductor side node528.

The various modes of operation of the configuration 500 operate asfollows. During recharge mode when using full wave rectification, theprocessor/controller 302 of this example sets the tuning switch 518 tothe state that provides the proper capacitance for setting the resonantfrequency of the tank circuit 416 to the recharge frequency. All otherswitches remain open. As a result, the current of the tank circuitpasses through the rectifier and on to the limiter and ultimately to thebattery 402. If half wave rectification is desired, then eithercapacitor low side switch 522 or inductor low side switch 524 is closed.

During recharge, one concern is that in an overcharge condition, thelimiter 552 increases impedance which pumps up voltage on the rectifierrecharge node 550 to a Schottky drop below the peak voltage on thecapacitor side node 526 and inductor side node 528. The peak voltage onthese two nodes is set by the Zener diodes 544, 546. If a large amountof energy continues to be coupled into the coil 504, then the Zenerdiodes 544, 546 may be subjected to significant heating which can beproblematic.

In such a case, the processor/controller 302 may detect such heating orovercharge via a temperature sensor 570 or other measurement device andrespond in various ways. For instance, the processor/controller 302 maychange the state of the tuning switch 518 so that the couplingcoefficient between the coil 504 and the coil of the external device 102is decreased, thereby decreasing the power being received. Additionallyor alternatively, the processor/controller 302 may close the capacitorlow side switch 522 and the inductor low side switch 524 to clamp thetank circuit 416 to ground, as the coil 504, capacitors 506, 510, andZener diodes 514, 516 together may be better suited to dissipate theheat as part of the larger system.

During telemetry downlink, where tuning to the telemetry frequency isdesired such as to establish an arm's length coupling at a time otherthan a recharge period, the processor/controller 302 of this examplesets the tuning switch 518 to the opposite state from that set forrecharge so that the proper capacitance for setting the resonantfrequency of the tank circuit 416 to the telemetry frequency isachieved. The tank switch 520 is then closed. All other switches areleft open, and the capacitor side node 526 and the inductor side node528 are allowed to float within a diode drop below ground and aboverectifier recharge node 550, respectively. The receiver 412 picks up thedifferential voltage across the coil 504. Several other methods oftelemetry downlink are discussed below with reference to other circuitdiagrams.

During telemetry downlink where the tuning may remain at the rechargefrequency, such as during a recharge period, the processor/controller302 of this example may maintain the tuning switch 518 in the same statethat is used for recharge so that the proper capacitance for setting theresonant frequency of the tank circuit 416 to the recharge frequency ismaintained. The tank switch 520 is then closed. All other switches areleft open, and the capacitor side node 526 and the inductor side node528 are allowed to float within a diode drop below ground and aboverectifier recharge node 550, respectively. The receiver 412 picks up thedifferential voltage across the coil 504 even though the tank circuit416 continues to be tuned to the recharge frequency. Furthermore, thetelemetry signals may be rectified to continue to provide some degree ofrecharge energy to the battery.

Maintaining the recharge switch in a closed state during downlinktelemetry limits high-voltage excursions on the high voltage node 508,which in turn limits the potential seen on the cathode of the Zenerdiode 514 which is AC coupled to high voltage node 508 via the rechargecapacitor 510. When the tuning switch 518 is closed, the potential onthe cathode of the Zener diode 514 is limited to a diode drop belowground and a diode drop above the voltage on the rectifier recharge node550. As such, there is no potential for anode connected Zener diodes514, 516 to activate, which is beneficial as Zener diodes 514, 516 areonly intended to operate occasionally.

During telemetry uplink, where tuning to the telemetry frequency isdesired such as to establish an arm's length coupling at a time otherthan a recharge period, the tuning switch 518 is set to tune the tankcircuit 416 to the telemetry frequency. The H-bridge may be operated byopening the capacitor high side switch 530 and the inductor low sideswitch 524 while the inductor high side switch 532 and the capacitor lowside switch 522 are closed. After a set amount of time defined by thetelemetry frequency, the inductor high side switch 532 and the capacitorlow side switch 522 are opened while the capacitor high side switch 530and the inductor low side switch 524 are closed. These pairings continueto alternate states to ring up the coil 504 at the telemetry frequencyand allow it to emit for a set amount of time. The capacitor low sideswitch 522 and the inductor low side switch 524 are then closed to ringdown the coil 504, which remains off for a set period until time toagain ring up the coil 504. In this manner, a carrier on/off protocolcan be effectively implemented to uplink data. As an alternative, thecoil 504 may be allowed to ring down by closing the tank switch 520,closing switches 522 and 524 or by opening all switches and allowing thetank to ring down at its natural frequency.

During telemetry uplink where the tuning may remain at the rechargefrequency, such as during a recharge period, the tuning switch 518 ismaintained to tune the tank circuit 416 to the recharge frequency. TheH-bridge may continue to be operated by opening the capacitor high sideswitch 530 and the inductor low side switch 524 while the inductor highside switch 532 and the capacitor low side switch 522 are closed. Aftera set amount of time defined by the telemetry frequency, the inductorhigh side switch 532 and the capacitor low side switch 522 are openedwhile the capacitor high side switch 530 and the inductor low sideswitch 524 are closed. These pairings continue to alternate states toring up the coil 504 at the telemetry frequency and allow it to emit fora set amount of time. The capacitor low side switch 522 and the inductorlow side switch 524 are then closed to ring down the coil 504, whichremains off for a set period until time to again ring up the coil 504.In this manner, a carrier on/off protocol can be effectively implementedto uplink data. As an alternative, the coil 504 may be allowed to ringdown by closing the tank switch 520, closing switches 522 and 524 or byopening all switches and allowing the tank to ring down at its naturalfrequency.

FIG. 20 shows a first timing chart for the H-bridge manner of telemetryuplink. The first waveform 2002 is a clock signal that is set to thetelemetry frequency. The second waveform 2004 is a clock signal that isset to double the telemetry frequency but is unused in this particularmethod. The third and fourth waveforms 2006, 2008 correspond to thestate of the capacitor low side switch 522 and the inductor low sideswitch 524, where a high value represents a closed state and a low valuerepresents an open state. The fifth and sixth waveforms 2010, 2012correspond to the state of the capacitor high side switch 530 and theinductor high side switch 532. The seventh waveform 2014 corresponds tothe state of the tank switch 520 which remains open in this example.

The eighth waveform 2016 corresponds to the current through the coil504. Sections 2018 and 2022 correspond to the ringing up and carrier onperiods, while section 2020 corresponds to the carrier off period.

FIG. 21 shows an alternative timing chart for the H-bridge manner oftelemetry uplink where the transmission power is being throttled down byreducing the drive time of the coil 504. In this particular example, thedrive time is being reduced by 50% by application of a clock frequencydouble that of the telemetry frequency, but other drive time reductionsare applicable. Throttling down the transmission power may be done forvarious reasons, such as to reduce the range of the transmission forsecurity or other purposes and/or to conserve energy. The drive time maybe reduced more or less than the 50% shown in FIG. 21 for similarreasons.

The first waveform 2032 is a clock signal that is set to the telemetryfrequency. The second waveform 2034 is a clock signal that is set todouble the telemetry frequency. The third and fourth waveforms 2036,2038 correspond to the state of the capacitor low side switch 522 andthe inductor low side switch 524, where a high value represents a closedstate and a low value represents an open state. The fifth and sixthwaveforms 2040, 2042 correspond to the state of the capacitor high sideswitch 530 and the inductor high side switch 532. The seventh waveform2044 corresponds to the state of the tank switch 520.

The eighth waveform 2046 corresponds to the current through the coil504. Sections 2048 and 2052 correspond to the ringing up and carrier onperiods, while section 2050 corresponds to the carrier off period.

As can be seen, the H-bridge switches are closed for half as long as inthe example of FIG. 20, and the tank switch 520 is closed for theremaining half of each telemetry clock cycle portion when all theH-bridge switches are open. As a result, the current in the coil 504rings up to a fraction of the amount of current achieved in the exampleof FIG. 20.

The telemetry uplink may be established in other ways as well by usingswitches on either side of the tank circuit 416 to ring the coil 504.For example, the capacitor low side switch 522 and the inductor highside switch 532 may be briefly closed, then opened while leaving theother switches open and then letting the tank circuit 416 ring down byclosing the tank switch 520 or by closing both the capacitor low sideswitch 522 and the inductor low side switch 524.

FIG. 6 shows a second configuration 600 which is identical to the firstconfiguration 500 of FIG. 5 except that a circuit pathway is providedthat includes a snubbing resistor 556 and a snubbing switch 554 that isunder control of the processor/controller 302 in parallel with the coil504. This circuit pathway provides power management in the event of anovercharge condition in addition to or as an alternative to the powermanagement methods discussed above for FIG. 5. Because the snubbingswitch 554 may be closed to allow some tank circuit current to passthrough the snubbing resistor to dissipate the energy as heat in thatcomponent and to lower the Q of the tank circuit 416, there is lessenergy to be dissipated by the Zener devices 542, 544 and 514, 516.

This circuit pathway including the snubbing switch 554 and snubbingresistor 556 may have other uses as well. For instance, the telemetry ofthe external device 102 may be configured to receive information bymonitoring for a change in the mutual inductance between the coil of theexternal device 102 and the coil 504 of the IMD 108 that is caused bythe IMD 108 while the external device 102 is emitting a signal. Thischange in the mutual inductance by the IMD 108 can be viewed as atransmission of information, for example where an on-off fashion of thechange in mutual inductance is similar to a carrier on-off protocol. Insuch a case, the H-bridge may be unnecessary and the capacitor high sideswitch 530 and inductor high side switch 532 may be omitted, althoughlow side switches 522 and 524 may be retained for other purposes such asto ground the tank circuit 416.

The circuit pathway including the snubbing switch 554 and the snubbingresistor 556 is shown in the configuration 600 of FIG. 6 as amodification to the configuration 500 of FIG. 5. However, it will beappreciated that this circuit pathway may be included as a modificationto other configurations as well, including those discussed below inrelation to FIGS. 7-19 and 22-24.

FIG. 7 shows another configuration 700 that is the same as theconfiguration 500 of FIG. 5 except that the receiver's connectivity isconfigured differently. In this example, a receiver input is coupleddirectly to the high voltage node 508, rather than being capacitivelycoupled through the second capacitor 510.

FIG. 8 shows another configuration 800 that is the same as theconfiguration 700 of FIG. 7 except that the receiver's connectivity isconfigured differently. In this example, a receiver input is coupleddirectly to the high voltage node 508, rather than being capacitivelycoupled through the second capacitor 510, but both the capacitor sidenode 526 and the inductor side node 528 are connected to ground byclosed switches 522′ and 524′ when receiving telemetry signals while allother switches are open.

FIG. 9 shows another configuration 900 that is the same as theconfiguration 500 of FIG. 5 except that the receiver's connectivity isconfigured differently. In this example, a receiver input iscapacitively coupled to the high voltage node 508 through the secondcapacitor 510, but both the capacitor side node 526 and the inductorside node 528 are connected to ground by closed switches 522′ and 524′when receiving telemetry signals while all other switches are open.

FIG. 10 shows another configuration 1000 that is the same as theconfiguration 800 of FIG. 8 except that the receiver's connectivity isconfigured differently. In this example, a receiver input is coupleddirectly to the high voltage node 508, rather than being capacitivelycoupled through the second capacitor 510, and both the capacitor sidenode 526 and the inductor side node 528 are connected to ground byclosed switches 522′ and 524′ when receiving telemetry signals while allother switches are open. However, the other input of the receiver 412 isconnected to the capacitor side node 526 rather than the inductor sidenode 528.

FIG. 11 shows another configuration 1100 that is the same as theconfiguration 900 of FIG. 9 except that the receiver's connectivity isconfigured differently. In this example, a receiver input iscapacitively coupled to the high voltage node 508 through the secondcapacitor 510, and both the capacitor side node 526 and the inductorside node 528 are connected to ground by closed switches 522′ and 524′when receiving telemetry signals while all other switches are open.However, the other input of the receiver 412 is connected to thecapacitor side node 526 rather than the inductor side node 528.

FIG. 12 shows another configuration 1200 that is the same as theconfiguration 500 of FIG. 5 except that the receiver's connectivity isconfigured differently. Here, the receiver is connected differentiallyacross the tank circuit 416 by having a receiver input coupled directlyto the inductor side node 528 while another receiver input is coupleddirectly to the capacitor side node 526. All other switches are openwhen receiving telemetry signals.

FIG. 13 shows another configuration 1300 that is the same as theconfiguration 500 of FIG. 5 except that the receiver's connectivity isconfigured differently. Here, one input of the receiver 412 remainsconnected to the inductor side node 528 while the other input of thereceiver 412 is connected to ground. All other switches are open whenreceiving telemetry signals or switch 520 may be closed.

FIG. 14 shows another configuration 1400 that is the same as theconfiguration 500 of FIG. 5 except that the receiver's connectivity isconfigured differently. Here, one input of the receiver 412 is connectedto the capacitor side node 526 while the other input of the receiver 412is connected to ground. All other switches are open when receivingtelemetry signals or switch 520 may be closed.

FIG. 15 shows another configuration 1500 that is the same as theconfiguration 500 of FIG. 5 except that the receiver's connectivity isconfigured differently. Here, one input of the receiver 412 is connectedto the additional capacitor side node 512 so as to be capacitivelycoupled to the high voltage node 508 while the other input of thereceiver 412 is connected to ground. All other switches are open whenreceiving telemetry signals or switch 520 may be closed.

FIG. 16 shows another configuration 1600 that is the same as theconfiguration 500 of FIG. 5 except that the receiver's connectivity isconfigured differently. Here, one input of the receiver 412 is connecteddirectly to the high voltage node 508 while the other input of thereceiver 412 is connected to ground. All other switches are open whenreceiving telemetry signals or switch 520 may be closed.

FIG. 17 shows a configuration 1700 that is the same as the configuration500 of FIG. 5 except that the rectifier is different. In thisconfiguration 1700, the rectifier may use both high side and low sidesynchronous rectification by including a capacitor high side rectifierswitch 558 and an inductor high side rectifier switch 560 in place ofhigh side diodes. As discussed for the configuration of FIG. 5, thecapacitor low side switch 522 and the inductor low side switch 524 mayoperate to provide the low side synchronous rectification.

In this particular example, the low side synchronous rectifier switches522, 524 may be N-MOS devices while the high side synchronous rectifierswitches 558, 560 may be P-MOS devices. The result based on the statemachine control by the processor/controller 302 is that when theinductor side flies high, the inductor high side switch 560 and thecapacitor low side switch 522 are closed while the capacitor high sideswitch 558 and the inductor low side switch 524 are open. When thecapacitor side flies high, the capacitor high side switch 558 and theinductor low side switch 524 are closed while the inductor high sideswitch 560 and the capacitor low side switch are open.

The synchronous rectifier of FIG. 17 may be a pure full wave synchronousrectifier as another alternative. In that case, the diodes 538 and 542are omitted.

While this operation of the switches 522, 524, 558, and 560 applies torecharge, during uplink and downlink telemetry operations, the capacitorlow side switch 522 and the inductor low side switch 524 may operate inthe same manner as discussed above in relation to FIG. 5. The capacitorhigh side switch 558 and the inductor high side switch 560 may remainopen during uplink and downlink telemetry operations.

FIG. 18 shows another configuration 1800 like the configuration 500 ofFIG. 5, except that the high side of the H-bridge created by thecapacitor high side switch 530 and inductor high side switch 532 hasbeen omitted. In this situation, the coil 504 is being used for rechargeand downlink telemetry. Uplink telemetry may be unnecessary in somecontexts for an IMD 108. As another example, uplink telemetry may beprovided at a separate frequency than downlink telemetry and may utilizea separate circuit and coil from that shown so that full-duplexcommunication with the external device 102 may be achieved. Thevariations discussed above in FIGS. 5-17 and below in FIGS. 22-24 arealso applicable to the configuration 1800 to the extent those variationsrelate to recharging, telemetry downlink, and power management.

FIG. 19 shows another configuration 1900 like the configuration 500 ofFIG. 5, except that the receiver 412 has been omitted. In thissituation, the coil 504 is being used for recharge and uplink telemetry.Downlink telemetry may be unnecessary in some contexts for an IMD 108.As another example, downlink telemetry may be provided at a separatefrequency than uplink telemetry and may utilize a separate circuit andcoil from that shown so that full-duplex communication with the externaldevice 102 may be achieved. The variations discussed above in FIGS. 5,6, and 17 and below in relation to FIGS. 22-24 are also applicable tothe configuration 1900 to the extent those variations relate torecharging, telemetry uplink, and power management.

FIG. 22 shows another configuration 2200 like the configuration 500 ofFIG. 5 except that the second capacitor 510 does not connect to the highvoltage node 508 while the receiver 534 is DC coupled to the highvoltage node 508. In this example, the coil 504 is provided with a tapcreating an intermediate node 509 and creating a first coil portion 507and a second coil portion 509. The second capacitor 510 connects to thetap in the coil providing the intermediate node 509. A voltage dividereffect is provided whereby the voltage at the intermediate node 509which AC couples to the node 512 and tuning switch 518 is less than thevoltage on the high voltage node 508. This provides additionalprotection to the tuning switch 518.

It will be appreciated that the selection of the capacitance for thesecond capacitor 510 will be different than the selection of thecapacitance for the second capacitor 510 in the configuration 500 ofFIG. 5 in order to tune to the same recharge frequency. It will also beappreciated that all of the variations discussed above in FIGS. 5-19 arealso applicable to the example of FIG. 22, including coupling thereceiver 412 to nodes besides the high voltage node 508.

FIG. 23 shows another configuration 2300 like the configuration 500 ofFIG. 5 except that the transmission switches 522, 524, 530, and 532 areno longer being used to ring the coil 504. Instead, an oscillator 521such as a sinusoidal power amplifier is connected across the tankcircuit 416 to drive the tank circuit at the uplink frequency. Theoscillator 521 may be activated and deactivated by the controller 302which may also switch the oscillator 521 into and out of the circuit.The capacitor high side switch 530 and the inductor high side switch 532may be omitted as shown. This oscillator 521 may result in fewerharmonics on the uplink carrier. It will be appreciated that all of thevariations discussed above in FIGS. 5-19 and 22 are also applicable tothe example of FIG. 23.

FIG. 24 shows another configuration 2400 like the configuration 500 ofFIG. 5 except that the variable reactance is provided by varying theinductance rather than the capacitance. The variable inductance isachieved in this example with the single coil 504 by providing a tap onthe coil 504 that establishes a first coil portion 507 and a second coilportion 509. The first coil portion is connected between the node 526and the high voltage node 508 while the second coil portion is connectedbetween a tuning switch 519 and the high voltage node 508. The tuningswitch 519 is further connected to the node 526. A first capacitor 506is connected between the high voltage node 508 and the node 528.

As can be seen by the dot convention of the coil 504, the first coilportion 507 and the second coil portion 509 are geometrically orientedso that their currents are directed in phase to the high voltage node508. This may be accomplished by changing the direction of the turns ofthe coil of the second coil portion 509 relative to the first coilportion 507, such as where a bobbin carrying both coil portions 507, 509is linear. As another example, this may be accomplished by maintainingthe direction of the turns about the bobbin but by reversing thedirection of the bobbin at the tap such as by having a U-shape.

The controller 302 operates the tuning switch 519 to switch the secondcoil portion 509 into and out of the tank 416. In doing so, thecontroller 302 is tuning the tank 416 either to the telemetry frequencyor to the recharge frequency. It will be appreciated that all of thevariations discussed above in FIGS. 5-19, 22 and 23 are also applicableto the example of FIG. 24.

FIG. 25 shows a first configuration 2500 for a circuit of the externalrecharge device 102′ that provides for telemetry uplink and downlink ata telemetry frequency during a recharge period with a tank circuit tunedto the recharge frequency. Like the configurations of the IMD 108, thefirst configuration 2500 includes switches implemented in silicon.

The first configuration includes the tank circuit 2516 that has a coil2504 and a fixed reactance that is provided by a fixed capacitance. Thefixed capacitance is achieved in this example by providing a firstcapacitor 2506 that is hardwired in series with the coil 2504.

The tank circuit 2516 establishes several nodes. An inductor side node2528, a capacitor side node 2526, and a high voltage node 2508 areachieved. The high voltage node 2508 acquires a relatively high voltageperiodically as the voltage swings within the tank circuit 2516.Capacitor low side switches 2522, 2540 and inductor low side switches2524, 2542 along with capacitor high side switch 2530 and inductor highside switch 2532 are also present and are discussed below. The switches2522, 2524, 2530, and 2532 form an H-bridge that can be used fortelemetry downlink to the IMD 108 as well as to emit recharge energy tothe IMD 108 where the switches 2530 and 2532 are connected to a voltagesource 2518 from the battery. The switches 2522 and 2524 provide astrong ground, i.e., low impedance to ground, for recharge and telemetrytransmission purposes while the switches 2540 and 2542 provide a weakground, i.e., higher impedance to ground, for telemetry receptionpurposes.

A capacitor side Zener diode 2544 and an inductor side Zener diode 2546are also present. These devices limit voltage swings on the capacitorside node 2526 and the inductor side node 2528 to prevent over-voltagedamage from occurring on voltage sensitive devices connected to thesenodes. Voltage sensitive devices may include the various switches whichare implemented in silicon and particularly those that are implementedas monolithic devices. As can be seen, no voltage sensitive device iscoupled to the high voltage node 2508 which reduces the likelihood ofany damage to those voltage sensitive devices.

This embodiment of the external recharge device 102′ is capable ofdirecting recharge energy to the IMD 108 by using the tank circuit 2516and one of various driver circuits and related methods, such as theH-bridge or an oscillator. For instance, as shown, the H-bridge may beused to transmit recharge energy by operating the H-bridge at therecharge frequency while the tank circuit 2516 is tuned to the rechargefrequency.

This embodiment of the external recharge device 102′ is capable oftelemetry uplink from the IMD 108 by using the tank circuit 2516. Thereceiver 2512 is present to receive the telemetry signals induced on thecoil 2504. The receiver 2512 is connected to the tank circuit 2516 in afirst configuration as shown. Other configurations are also availablesuch as those similar to the configurations for the receiver of the IMD108 in FIGS. 6-19 and 22-24. In this example, a first input of thereceiver 2512 is connected to the capacitor side node 2526 while anotherinput is grounded. As the input impedance of the receiver 2512 is veryhigh, the receiver 2512 does not appreciably affect the tuning of thetank circuit 2516. Low side switches 2540 and 2542 are present to weaklycouple the tank circuit 2516 to ground when receiving telemetry.

This embodiment of the external recharge device 102′ is also capable oftelemetry downlink to the IMD 108 by using the tank circuit 2516 and oneof various driver circuits and related methods. For instance, as shown,the H-bridge may be used to transmit telemetry signals by operating theH-bridge at the telemetry frequency even though the tank circuit 2516remains tuned to the recharge frequency.

The various modes of operation of the configuration 2500 operate asfollows. During recharge mode, the processor/controller 202 of thisexample operates the H-bridge or other driver circuit at the rechargefrequency to drive the tank circuit 2516 to emit recharge energy at therecharge frequency by opening the capacitor high side switch 2530 andthe inductor low side switch 2524 while the inductor high side switch2532 and the capacitor low side switch 2522 are closed. Switches 2450and 2542 remain open during recharge mode. After a set amount of timedefined by the recharge frequency, the inductor high side switch 2532and the capacitor low side switch 2522 are opened while the capacitorhigh side switch 2530 and the inductor low side switch 2524 are closed.These pairings continue to alternate states to ring up the coil 2504 atthe recharge frequency and allow it to emit for a set amount of time.The capacitor low side switch 2522 and the inductor low side switch 2524are then closed to ring down the coil 2504, which remains off for a setperiod until time to again ring up the coil 2504. As an alternative, thecoil 2504 may be allowed to ring down by closing a tank switch that maybe included but is not shown in this example, by closing switches 2522and 2524 or by opening all switches and allowing the tank to ring downat its natural frequency.

During telemetry uplink occurring in the recharge period, theprocessor/controller 202 of this example leaves all switches open exceptcapacitor low side switch 2540 and inductor low side switch 2542 areclosed to weakly ground the capacitor side node 2526 and the inductorside node 2528, thereby grounding both sides of the tank circuit 2516through a small additional impedance. This weak ground effectivelylowers the Q of the tank circuit 2516 to widen the bandwidth forreceiving telemetry signals. The receiver 2512 picks up the differentialvoltage between a node of the tank circuit 2516, node 2526 in thisexample, and ground.

During telemetry downlink, the processor/controller 202 operates theH-bridge by opening the capacitor high side switch 2530 and the inductorlow side switch 2524 while the inductor high side switch 2532 and thecapacitor low side switch 2522 are closed. Switches 2540 and 2452 remainopen during telemetry downlink. After a set amount of time defined bythe telemetry frequency, the inductor high side switch 2532 and thecapacitor low side switch 2522 are opened while the capacitor high sideswitch 2530 and the inductor low side switch 2524 are closed. Thesepairings continue to alternate states to ring up the coil 2504 at thetelemetry frequency and allow it to emit for a set amount of time. Thecapacitor low side switch 2522 and the inductor low side switch 2524 arethen closed to ring down the coil 2504, which remains off for a setperiod until time to again ring up the coil 2504. In this manner, acarrier on/off protocol can be effectively implemented to downlink data.As an alternative, the coil 2504 may be allowed to ring down by closinga tank switch that may be included across the tank circuit 2516, byclosing switches 2522 and 2524 and/or switches 2540, 2542, or by openingall switches and allowing the tank to ring down at its naturalfrequency.

FIG. 26 shows an example of logical operations that may be performed bythe external recharge device 102′ and the IMD 108 when conductingrecharge and telemetry during a recharge period. Initially, the IMD 108of this example may be in a default state where the tank circuit of theIMD 108 is tuned to the telemetry frequency so that the IMD 108 mayexchange telemetry with an external telemetry device 101. The externalrecharge device 102′ downlinks an instruction at the telemetry frequencyto switch to recharge frequency tuning at a downlink operation 2602 thatbegins the recharge period. The IMD 108 receives and implements theinstruction to change the state from the telemetry frequency tuning,i.e. arm's length tuning (ALT), to recharge frequency tuning and turnson the receiver decoders at a tuning operation 2604. The IMD 108 mayalso uplink an acknowledgement (ACK) to the external recharge device102′ at the telemetry frequency with the tank circuit tuned to therecharge frequency.

The external recharge device 102′ then begins to stream recharge energyat the recharge frequency at a recharge operation 2606. The externalrecharge device 102′ then begins detecting whether a set period of time,such as ten seconds, has expired at a query operation 2608. If the setperiod of time has not expired, then the external device 102′ continuesto stream the recharge energy. If the set period of time has expired,then the external device 102′ downlinks a request for recharge relatedstatus information at the telemetry frequency at a downlink operation2610. Because the IMD 108 is capable of receiving the downlink at thetelemetry frequency while the tank circuit of the IMD 108 is tuned tothe recharge frequency, there is no need to use a timing guardbandand/or handshake to establish telemetry communications because the IMD108 may be continuously monitoring for telemetry communications whilethe recharge energy is streaming. Thus, the IMD 108 receives the requestfrom the external recharge device 102′ and then uplinks the statusinformation, such as coulomb counter (cc) information, temperature, andthe like using the telemetry frequency while the tank circuit is tunedto the recharge frequency at an uplink operation 2616.

The external recharge device 102′ receives the uplink of statusinformation and then detects from that information whether more rechargeis needed at a query operation 2614. If more recharge is needed, thenthe external recharge device 102′ initiates the streaming of rechargeenergy at the recharge operation 2606. The IMD 108 continues to be in arecharge state where the tank circuit is tuned to the recharge frequencysuch that when the streaming of recharge energy resumes, the IMD 108immediately receives and rectifies the recharge energy to recharge thebattery. If more recharge is not needed, then the external rechargedevice 102′ downlinks an instruction to switch to telemetry tuning tothe IMD 108 using the telemetry frequency. The IMD 108 receives andimplements the instruction to tune the tank circuit to the telemetryfrequency for ALT at a tuning operation 2618. The IMD 108 may also turnoff the decoders of the receiver and may also uplink an ACK using thetelemetry frequency. The external recharge device 102′ receives the ACKand then terminates operation for the recharge session occurring duringthis recharge period at a completion operation 2610.

At a second time period that is prior to and/or subsequent to a firsttime period during which these operations of FIG. 26 are beingperformed, the external device 101 may initiate a telemetry session withthe IMD 108. In this example, the IMD 108 is already tuned to thetelemetry signal prior to and subsequent to the operations of FIG. 26such that the IMD 108 is ready to begin the telemetry session uponrequest by the external device 101. Thus, when the external device 101communicates with the IMD 108, the IMD 108 has the tank circuit tuned tothe telemetry frequency which will provide maximum signal couplingbetween the two devices and which may allow for arm's length telemetry.

While embodiments have been particularly shown and described, it will beunderstood by those skilled in the art that various other changes in theform and details may be made therein without departing from the spiritand scope of the invention.

What is claimed is:
 1. An external recharge device, comprising: a tankcircuit tuned to a recharge frequency of recharge energy; a receiverwith at least one input electrically connected to a node of the tankcircuit, the receiver being configured to receive from the tank circuitincoming telemetry signals at a telemetry frequency; a driver circuitelectrically connected to a node of the tank circuit; and a controllerin electrical communication with the driver circuit, the controllercausing the driver circuit to drive the tank circuit at the rechargefrequency when sending recharge energy and to drive the tank circuit ata telemetry frequency when sending outbound telemetry signals.
 2. Theexternal recharge device of claim 1, wherein the controller is furtherconfigured to send an instruction via the outbound telemetry signals,wherein the instruction is a request that an implantable medical devicetune a receiving circuit of the implantable medical device to therecharge frequency.
 3. The external recharge device of claim 2, whereinthe controller is further configured to send an instruction via theoutbound telemetry signals, wherein the instruction is a request thatthe implantable medical device report a recharging status.
 4. Theexternal recharge device of claim 3, wherein the controller sends theinstruction to request that the implantable medical device report arecharging status after an amount of time has passed since sendingrecharging energy.
 5. The external recharge device of claim 1, whereinthe controller is further configured to send an instruction via theoutbound telemetry signals, wherein the instruction is a request that animplantable medical device tune a receiving circuit of the implantablemedical device to the telemetry frequency.
 6. A medical system,comprising: an external recharge device that transmits recharge energyat a recharge frequency from a tank circuit tuned to the rechargefrequency and that exchanges telemetry signals at a telemetry frequencythat is different than the recharge frequency through the tank circuittuned to the recharge frequency; and an implantable medical device thatreceives recharge energy at the recharge frequency from a tank circuittuned to the recharge frequency and that exchanges telemetry signals atthe telemetry frequency through the tank circuit tuned to the rechargefrequency.
 7. The medical system of claim 6, wherein the externalrecharge device sends telemetry signals including an instruction and theimplantable medical device receives and implements the instruction totune the tank circuit of the implantable medical device to the rechargefrequency.
 8. The medical system claim 7, wherein the implantablemedical device receives the instruction from a telemetry signal at thetelemetry frequency while the tank circuit of the implantable medicaldevice is tuned to the telemetry frequency.
 9. The medical system ofclaim 6, wherein the external recharge device sends telemetry signalsincluding an instruction and the implantable medical device receives andimplements the instruction to tune the tank circuit to the telemetryfrequency.
 10. The medical system of claim 9, wherein the implantablemedical device receives the instruction from a telemetry signal at thetelemetry frequency while the tank circuit of the implantable medicaldevice is tuned to the recharge frequency.
 11. The medical system ofclaim 6, wherein the tank circuit of the implantable medical device istuned to the recharge frequency while receiving the telemetry signalsduring a first time period, and is tuned to the telemetry frequencywhile receiving the telemetry signals during a second time period thatis distinct from the first time period.
 12. The medical system of claim11, wherein the tank circuit of the implantable medical device is tunedto the recharge frequency while the rectifier is receiving the rechargeenergy during the first time period.
 13. The medical system of claim 11,further comprising an external telemetry device that exchanges telemetrysignals at the telemetry frequency with the implantable medical devicethrough a tank circuit of the external telemetry device that is tuned tothe telemetry frequency.
 14. A method, comprising: transmitting by anexternal device recharge energy at a recharge frequency from a tankcircuit tuned to the recharge frequency and that exchanges telemetrysignals at a telemetry frequency that is different than the rechargefrequency through the tank circuit tuned to the recharge frequency; andreceiving by an implantable medical device recharge energy at therecharge frequency from a tank circuit of the implantable medical devicethat is tuned to the recharge frequency and that exchanges telemetrysignals at the telemetry frequency through the tank circuit tuned to therecharge frequency.
 15. The method of claim 14, wherein the externalrecharge device sends telemetry signals including an instruction and theimplantable medical device receives and implements the instruction totune the tank circuit of the implantable medical device to the rechargefrequency.
 16. The method of claim 15, wherein the implantable medicaldevice receives the instruction from a telemetry signal at the telemetryfrequency while the tank circuit of the implantable medical device istuned to the telemetry frequency.
 17. The method of claim 16, whereinthe external recharge device sends telemetry signals including aninstruction and the implantable medical device receives and implementsthe instruction to tune the tank circuit to the telemetry frequency. 18.The method of claim 17, wherein the implantable medical device receivesthe instruction from a telemetry signal at the telemetry frequency whilethe tank circuit of the implantable medical device is tuned to therecharge frequency.
 19. The method of claim 14, wherein the tank circuitof the implantable medical device is tuned to the recharge frequencywhile receiving the telemetry signals during a first time period, and istuned to the telemetry frequency while receiving the telemetry signalsduring a second time period that is distinct from the first time period.20. The method of claim 17, wherein the tank circuit of the implantablemedical device is tuned to the recharge frequency while the rectifier isreceiving the recharge energy during the first time period.